N-15 NUCLEAR MAGNETIC-RESONANCE OF ORGANOPHOSPHORUS COMPOUNDS - RING SIZE AND AZIRIDINE METHYLATION EFFECTS ON N-15 SHIFTS AND N-15-P-31 NUCLEAR-SPIN COUPLINGS IN HETEROCYCLIC PHOSPHORAMIDATES

Natural abundance 15N NMR studies have been carried out on a series of cyclic phosphoramidates, including several methylated three-membered ring versions. The three-membered ring aziridine phosphoramidate was observed to have a substantial shielding (34 ppm) with respect to larger ring systems. Large β-substituent effects on the 15N shift were noted along with changes in directly bonded 15N-31P couplings from 9.3 Hz in the nonsubstituted three-membered ring compound to ≤1 Hz in the fully substituted 2, 2, 3, 3-tetramethylphosphoramidate. This directly bonded coupling experiences a large increase in going to the larger ring system, reflecting the change from a pyramidal-like (sp3) nitrogen in the three-membered ring to trigonal (sp2) in the larger ring compounds and the acyclic (diethylamino)dimethylphosphoramidate, where the observed coupling is 42.2 Hz. © 1979, American Chemical Society. All rights reserved.